Method of producing grain-oriented electrical steel



United States Patent 3,151,005 METHOD OF PRODUCING GRAIN-GRAENTED ELECTRICAL STEEL Harry M. Alworth and Harry F. Shannon, Monroeville Borough, Allegheny County, and Edward B. Stanley, Washington Township, Westmoreland County, Pa., assignors to United States Steel Corporation, a corporation of New Jersey No Drawing. Filed Mar. 13, 1961, Ser. No. 94,965

16 Clmms. (Cl. 148-111) This invention relates to the production of grainoriented electrical steel in sheets or coils having a {110)[001], or cube-on-edge, texture and more particularly to a method of producing grain-oriented electrical steel having improved magnetic properties.

Silicon steel containing about 2.75 to 3.5 percent silicon (sometimes referred to as the 3.25% silicon grade) is conventionally treated by a double cold reduction with each cold reduction followed by a continuous anneal, and thereafter a high temperature box anneal, which sequence of steps develops a grain-oriented sheet product with highly directional magnetic properties. Aside from the foregoing treatment, it is known that the condition of the steel prior to cold rolling has some effect on the subsequent degree of orientation. While various hotrolling conditions leading to some improvement in the resulting electrical properties have been proposed, the effect thereof has not been consistently reproducible.

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controlling the cooling cycle from a solution-annealing temperature, the structure of the steel can be varied to exhibit grain-boundary carbides only, a mixture of grainboundary carbides and spheroidal and lenticular matrix precipitates, lenticular precipitates only, or no precipitates. The effect of the variations in microstructure on the final magnetic properties of grain-oriented steel, as obtained by different controlled practices of cooling hotrolled silicon steel prior to treating to develop grain orientation by two cold reductions with intermediate and final anneals, is shown in Table I.

The core loss and A.-C. permeability values given in Table I, and in subsequent tables, were determined by the Epstein test method as described in Designation A-343-54 of the American Society for Testing Materials, 1958 Book of ASTM Standards, Part 3. The amount of anisotropy developed in the samples was determined by the well-known torque-magnetometer test. In this test, a single crystal of 3.25 percent silicon steel with cubeon-edge texture exhibits asymmetrical major peaks in the magnetic-torque curve with values of 200,000 dynecm./c1n. In Table I the maximum magnetic-torque values of the samples are expressed as percentages of the value obtained for the single crystal. The composition (ladle analysis) of steel used to study these effects was, in percent: carbon 0.020, manganese 0.08, phosphorus 0.004, sulphur 0.015, silicon 3.38, and remainder iron except for residual impurities.

Table 1 Average Average Average a-c Microstructure Cooling practice anisotropy, core loss, pcrmeapercent w.,llb./l5 bility at kg./00 15kg.

Predominantly grain-boundary Rapid cool from 1,750 F. to 1,200 v52 0. 88 5, 775

carbides F., heated at 1200 F. for 1 hour,

then air cooled. Mixture oigrain-boundary carbides Air cooled from 1,750 F. to room 59 0. 78 9, 941

and spheroidal and lenticular temperature. matrix precipitates. No Visible precipitates Quenched from 1,750 F. to room 65 0. 76 9. 938

temperature. Predominantly lonticular precipi- Rapid cool from 1,750 F. to 800 74 0.64 19,530

totes. F., heated at 800 F. for 1 hour,

then air cooled.

It is accordingly an object of this invention to provide a silicon electrical steel having improved magnetic properties and a more highly developed cube-on-edge texture.

It is another object of this invention to provide an improved treatment for producing grain-oriented electrical sheet product. i

It is a further object of this invention to provide an improved composition for steels treated to develop a grain-oriented structure therein.

We have discovered a significant improvement can be made in the degree of orientation and in the resulting magnetic properties developed during final high-temperature annealing if the hot-rolled band of 3.25 percent grade silicon steel is subjected to a critical treatment prior to the first cold reduction. This grade of steel has contained 0.05 percent maximum carbon (0.03% maximum preferred), 0.15 percent maximum manganese, 2.75 to 3.5 percent silicon, with the balance iron and residual amounts of other elements. Our discoveries relate to the eifect of certain carbides or precipitates in the hot-rolled strip on the final grain orientation and magnetic properties. We have discovered that grain-boundary carbides are harmful to the development of a high degree of cube-onedge orientation and best magnetic properties, whereas a lenticular-type carbide precipitate within the grains has a beneficial eifect. We have further discovered that by The data of Table I show that to obtain a high degree of preferred orientation and improved magnetic properties, a microstructure in which there are lenticular precipitates within the grains and no carbides at the grain boundaries should be provided in the hot-rolled steel before the first cold reduction.

The undesirable grain-boundary precipitate forms in a vary short time at relatively high temperatures. However, by heating the hot-rolled steel to above about 1450" F. and preferably at about 1550 F. to 1750 F, holding for at least 10 minutes to place carbon in solution, and then quenching drastically to maintain carbon in solution, the formation of the precipitate can be prevented. The expression quenching drastically is defined as cooling the steel at a rate suiiiciently fast to avoid the formation of the undesirable high-temperature grain-boundary precipitates, e.g., at a rate greater than F./sec. and preferably at a rate of at least about F./sec., a preferred rate being about F./sec. After this socalled solution treatment, there are no precipitates of either type visible when the steel is viewed under a light microscope at high magnification. If hot-rolled strip with this microstructure, no precipitates, is processed into grainoriented steel, the magnetic properties are somewhat better than those of steel processed from hot-rolled strip With grain-boundary precipitates.

The desirable lenticular precipitates are developed by holding, for a short time at relatively low temperatures (below about 1000 F.), steel which has been solution treated at a temperature of above about 1450 F. and preferably in the range of 1550 F. to 1750 F. to place the carbon in solution and then quenched to below f1000 F. from such temperatures or at least from a temperature in the neighborhood of 1450 F., to prevent the agglomeration of carbides at the grain boundaries. Thus we may first heat the steel to a temperature in the range of 1450 F. to 1750 F., then rapidly quench the steel to a temperature in the range of 600 F. to 1000 F., then hold the steel within the latter range for a time suflicient to develop the desired lenticular precipitates. Such precipitates can also be produced by reheating to about 800 F. steel that has been solution-treated and quenched to below 600 F. and holding the steel at that temperature for 10 minutes or longer. Hot-rolled strip given this precipitation treatment after a solution treatment and then processed into grain-oriented steel by conventional treatment has better properties than steel processed from hot-rolled strip given only the solution treatment. The results of three trials on strip of the same steel as that of Table I are summarized in the following Table II.

Table 11 Magnetic Properties of Fully Processed Steel Pro-Treatment of Hot-Rolled Strip Core loss, A.C. Perw./lb./ meability Anistropy, 15 kg./60 at 15 Kilopercent gauss Trial A:

a. None 0.80 8,758 40 b. Solution Treatment 1 0.76 9, 218 64 c. Solution and Precipitation Treatment 2 O. 65 16, 681 77 Trial B:

a. None V 0. 84 4, 799 51 b. Solution Treatment 1 0.79 8, 441 60 0. Solution and Precipitation Treatment 2 0. (i7 15, 234 80 Trial 2.. None 0. 77 8, 758 52 1). Solution Treatment 1 0.77 8, 544. 61 0. Solution and Precipitation Treatment 2 0.65 15, 923 67 1 Solution Treatment. Heat to 1,550 F.hold for 10 minutes at termperatureWater quench.

2 Precipitation Treatment. 'Rehcat to 800 F.ho1d for 10 minutes at temperature-Air cool.

We have established that the solution treatment can be conducted by holding the steel for from 1 to 60 minutes at temperatures in the range of 1450 F. to 1750 F. The longer holding times are necessary at the lower temperatures and, conversely, only short holding times are required at the higher temperatures.

We have also found that the precipitation treatment can be conducted at temperatures of 600 F. to 900 F. and with holding times of -1 minute to 120 minutes or even longer, the shorter times being used with the higher temperatures and the longer times with the lower temperatures.

i Both the solution treatment and the precipitation treatment may be conducted by controlling the cooling of the steel through the temperature ranges involved at a sufiiciently slow rate rather than holding the steel at specified temperatures in these ranges. Thus, in one advantageous method of practicing our invention, the hot-rolled band leaving the finishing stand of a hot mill at a finishing temperature above 1700 F., and preferably of about 1750. F may cool to about 1450 F. before it is watersprayed to quench it to about 800 F., preferably at a rate in excess of 120 F ./sec., and finally coiled at about this temperature and cooled in coil form through the precipitation-treatment temperature range.

After the hot-rolled band, which may have a thickness of about 0.075 to 0.090 inch, is treated as described in a decarburizing atmosphere with a dew point of about +70 F. Thereafter, the steel is box annealed at a temperature above 2000 F. in a dry, preferably hydrogen, atmosphere. Following such treatment, if pretreated in accordance with our invention, the steel will have a well defined grain-oriented structure and optimum magnetic properties. 7

We have also discovered that additional benefits and improvements are obtained if ladle carbon contents above about 0.04 percent are used, and preferably within the range of 0.04 to 0.065 percent, provided the carbon content is reduced below 0.003 percent no later than in the second continuous anneal. Also a ladle carbon content up to 0.085 percent may be used, provided the carbon content of the steel strip is at least reduced to below 0.065 percent in the first continuous anneal and to below 0.003 percent in the second continuous anneal. Experiments conducted with steels of the following composition illustrate the benefits derived from practicing proper carbon control.

Table III Steel 0 Mn S Si N 0. 0085 0. 11 0. 0045 3. 28 0. 001 0. 016 0. 11 0.0135 2. 82 0. 001. 0. 024 0. 04 0. 004 3. 31 0. 003 0. 029 0. 0i 0.007 8.30 0.001 0. 041 0. 12 0. 010 2. 0.009 0. 04 0. 04 0. 014 3. 24 0. 007 0. 061 0.07 0. 013 3. 38 0.005 0. 065 0. l1 0. 014 2. 89 O. 007 0. 091 0. 08 0. 015 2. 69 0. 009 0. 0. 16 0. 013 3. 38 0. 006 0.11 0.16 0. 018 2. 51 0. 00d

Small vacuum-melted laboratory-sized ingots of these steels were hot charged into a reheat furnace, heated for 1 hour at 2350 F., and then hot rolled to one-inch-thick plates in three passes. After being air cooled to room temperature and surface conditioned, a section of the plate representing each heat was reheated to 25 50 F. and then hot rolled to 0.080-inch-thick strip in three passes with a finishing temperature (temperature before last pass) of about 1750 F. The strip was cooled rapidly (about 8 seconds) to about 800 F. by water spraying the strip as it emerged from the rolls on the hot mill. The strip was then immediately inserted into a furnace, and the temperature of the steel was maintained at 800 F. for 1 hour before it was permitted to cool to room temperature. This treatment produced the desired lenticular carbides within the grains except in Steel A, which has a low carbon content approaching the solubility of carbon in ferrite.

After being descaled, the 0.080-inch-thick strip was cold reduced to an intermediate thickness of 0.028 inch in four passes. The cold-reduced strip was then heat treated in a protective atmosphere at 1600 F. for about 2 minutes. Following this heat treatment, the steel was cold reduced to a final thickness of 0.014 inch in 2 passes and then decarburized in a subsequent heat treatment which was conducted at about 1475 F. for 5 minutes in a moist hydrogen-nitrogen gas mixture having a dew point of about +70 F. The carbon content of the double cold reduced and annealed steel, regardless of the initial variation in carbon content, was about 0.002 percent or less. Epstein samples prepared from the decarburized and recrystallized sheet samples were annealed at 2150 F. for" 7 /2 hours in dried hydrogen. Magnetic-property tests, results of which appear in the following table, were conducted on these annealed Epstein samples.

These results clearly show that at least 0.01 percent carbon is required if any benefit is to be obtained in practicing this invention, and that carbon must be present in the steel through the first cold reduction in the amount of 0.04 to 0.065 percent if the superior magnetic properties and a high degree of preferred orientation of this invention are to be developed in grain-oriented silicon steel. In addition to the beneficial effect of carbon in such range, we have discovered that carbon up to 0.085 percent can be tolerated in the hot-rolled strip, provided the steel is decarburized to at least 0.065 percent during the continuous anneal after the first cold reduction. For example, steel containing 3.33 percent silicon and having 0.082 percent carbon was first treated to produce the desired carbide structure and decar'ourized to about 0.065 percent in the anneal following the first cold reduction. The final core loss of this steel was 0.63 w./lh./ kg;./ 60 and the AC. permeability at 15 kg. was 23,43 8.

We do not know the exact mechanism by which the beneficial effect of the lenticular precipitates in the hotrolled strip is realized. We believe, however, that these relatively large particles may have, no effect per se but, rather, may be only an indication of the existence of a condition favorable for the development of the desired grain orientation. Possibly, this favorable condition could be one in which very fine carbide precipitates are ideally disposed on crystallographic planes.

Although lenticular carbide matrix precipitates are formed in steels of higher carbon content (e.g.,,Steels I through K), such steels also contain, after the treatment, an abundance of austenite transformation products that appear, in the higher amounts involved when the ladle C content exceeds 0.065 percent, to have a detrimental effect on the properties of the product sheets. Although it is generally believed that such transformation products are undesirable in steel for electrical sheets, We have surprisingly discovered that in the quantities involved when the ladle carbon content was in the preferred range 0.04 to 0.065 percent, such transformation products appear to-have a desirable effect.

This application is a continuation-impart of our copending application Serial No. 825,889, filed July 9, 1959, now abandoned.

While we have shown and described several specific embodirnents of our invention, it will be understood that these embodiments are merely for the purpose of illustration, and description and that various other forms may be devised within the scope of our invention, as defined in the appended claims. r

We claim: r

1. A method of treating hot-rolled silicon electrical steel containing at least .01 percent: carbon prior to cold reducing and annealing to develop grain orientation and magnetic properties. comprising bringing such steel to a temperature between l450 F. and 1750 F. to place the carbon in solution, drastically quenching it from such temperature to a temperature less than 1000 F. to maintain the carbon in solution and prevent carbide agglomeration at the grain boundaries, holding within the range of 600 F. to 900 F. for suflicient time to develop lenticular precipitates within the grains and thereafter cooling to room temperatures.

2. A method of treating hot-rolled silicon electrical steel containing at least .01 percent carbon prior to cold reducing and annealing to develop grain orientation and magnetic properties comprising bringing such steel to a temperature between 1450 F. and 1750 F. to place the carbon in solution, drastically quenching it from such temperature at a rate in excess of F./sec. to a temperature less than 1000 F. to maintain the carbon in solution and prevent the agglomeration of carbides at the grain boundaries, holding within the range of 600 F. to 900 F. for l to minutes for suliicient time to develop lenticular precipitates within the grains and cooling to room temperature.

3. A method of treating hot-rolled silicon electrical steel containing between .04 and .065 percent carbon prior to cold reducing and annealing to develop grain orientation therein comprising bringing such steel to a temperature between 0 F. and 1750 F. to place the carbon in solution, drastically quenching from such temperature to about. 800 F. at a rate of about F./sec. to maintain the carbon in solution and prevent agglomeration of carbides at the grain boundaries, holding at about 800 F. for about 10 minutes to develop lenticular precipitates within the grains and thereafter cooling to room temperature.

4. A method of producing grain-oriented electrical steel comprising hot-rolling silicon steel containing at least .01 percent carbon and about 2.75 to 3.50 percent silicon to. produce a hot-rolled band, bringing said band to a temperature between 1450 F. and 1750 F. to place the carbon in solution, drastically quenching from such temperature at a rate in excess of 75 F./sec. to a temperature less than 1000 F. to maintain the carbon in solution and prevent the agglomeration of carbides .at the grain boundaries, holding within the range of 600 F. to 900 F. for sufiicient time to develop lenticular precipitates within the grains and then alternately cold reducing and annealing said band to develop a grain-oriented structure therein.

5. A method of producing grain-oriented electrical steel comprising hot-rolling silicon steel containing at least .01 percent carbon and about 2.75 to 3.50 percent silicon to produce a hot-rolled band, bringing said band to a temperature between 1450 F. and 1750 F. to place the Carbon in solution, drastically quenching from such temperature at a rate at least greater than 75 F./sec. to a temperature less than 1000 F. to maintain the carbon in solution and prevent the agglomeration of carbides at the grain boundaries, holding within the range of 600 F. to 900 ,F. for 1 to 120 minutes for suflicient time to develop lenticular precipitates within the grains and then alternately cold reducing and annealing said band to develop grain orientation.

6. A method of producing grain-oriented electrical steel comprising hot-rolling silicon steel containing between .04 and .065 percent carbon and about 2.75 to 3.50 percent silicon toproduce 'a hot-rolled band, heat treating said band at a temperature between 1450 F. and 1750 F. to place the carbon in solution, drastically quenching from such temperature at a rate in excess of 120 F./ sec.

to about 800 F. tormaintain the carbon in solution and prevent the agglomeration of carbides at. the grain boundaries, holding at about 800 F. for about: 10 minutes to develop lenticular carbides Within the grains and then alternately cold reducing and annealing said band to develop grain orientation.

7. A method of producing grain-oriented electrical steel comprising hot-rolling silicon steel consisting of .04 to .065 percent carbon, .15 percent maximum manganese, 2.75 to 3.50 percent silicon with the balance iron and residual amounts of other elements to produce a hotrolled band having a gauge of .075 to .090 inch, bringing said band to a temperature between 1450 F. and 1750 F. to place the carbon in solution, drastically quenching from such temperature at a rate of about 150 F./sec. to about 800 F. to maintain the carbon in solution and prevent the agglomeration of carbides at the grain boundaries, holding at about 800 F. for about minutes to develop lenticular carbides within the grains, cold reducing the pretreated band to between .020 to .030 inch gauge, continuously annealing at a temperature between 1600 F. and 1725 F., cold reducing to final gauge, continuously annealing at a temperature between 1400 F. and 1500 F. in an atmosphere containing at least 2 percent water vapor to reduce the carbon content to less than .003 percent and thereafter box annealing at a temperature above 2000 F. to develop a grain-oriented structure therein having enhanced magnetic properties.

8. A method of producing grain-oriented electrical steel comprising hot-rolling silicon steel containing .04 to .065 percent carbon, .15 percent maximum manganese, 2.75

to 3.50 percent silicon with the balance substantially iron 7 to produce a hot-rolled band having a gauge of .075 to .090 inch, finishing said hot rolling at a temperature above '1700 F. to bring the carbon into solution, thereafter drastically quenching it at a rate in excess of 120 F. per second to a temperature less than 1000 F. to maintain the carbon in solution and prevent the agglomeration of carbides at the grain boundaries, coiling said band at such temperature and then slowly cooling in coil form to less than 600 F. to develop lenticular precipitates within the grains and then alternately cold reducing and annealing said band to develop a grain-oriented structure therein.

' 9. A method of producing grain-oriented electrical steel comprising hot-rolling silicon steel containing .04 to .065

percent carbon, .15 percent maximum manganese, 2.75

to 3.50 percent silicon with the balance iron and residual amounts of other elements to produce a hot-rolled band having a gauge of .075 to .090 inch, finishing said rolling at a temperature of about 1750 F. to place the carbon in solution, drastically quenching said hot-rolled band from a temperature in excess of 1450 F. at a rate of about 150 F./sec. to about 800 F. to maintain the carbon in solution and prevent the agglomeration of carbides at the" grain boundaries, coiling said band at about 800 F., and then slowly cooling said coil to less than 600 F. to develop lenticular precipitates within the grains and then alternately cold reducing and annealing said band to develop grain orientation.-

10. In the method of producing grain-oriented electrical steel characterized by improved grain orientation and magnetic properties which includes hot-rolling silicon steel containing at least 01% carbon to produce a hotrolled band and thereafter cold reducing and annealing said hot-rolled band to develop a grain-oriented structure therein, the improvement comprising finishing the hot rolling at a temperature above 1700 F. to provide a structure having the carbon in solution, thereafter drastically quenching it at a rate in excess of 120 F. per second to a temperature less than 1000 F. to maintain thecarbon in solution. and preventthe agglomeration of carbides at the grain boundaries, coiling said band and then slowly cooling it in coil form within the range of 600 F. to 900 F., to develop lenticular precipitates within the grains prior to cold reducing and annealing said band to develop a grain-oriented structure therein.

11. In the method of producing grain-oriented electrical steel characterized by improved grain orientation and magnetic properties which includes hotwrolling silicon steel containing at least .01 percent carbon and about 2.75 to 3.50 percent silicon to produce a hot-rolled band and thereafter. coldreducing and annealing said band to dey velop agrain-oriented structure therein, the improvement comprising bringing said hot-rolled band to atemperature between 1450 F. and 1750.F. to place the carbon in solution, drastically quenching from such temperature at a rate in excess of 75 F./ sec. to a temperature less than 1000 F. to maintain the carbon in solution and prevent the agglomeration of carbides at the grain boundaries and then holding the hot-rolled band within the range of 600 F. to 900 F. for sufiicient time to develop lenticular precipitates within the grains prior to treating said band to develop the desired grain orientation.

12. In the method of producing grain-oriented electrical steel which includes hot-rolling silicon steel containing at least .01 percent carbon and about 2.75 to 3.50 percent silicon to produce a hot-rolled band and thereafter cold reducing and annealing said hot-rolled band to develop a grain-oriented structure therein, the improvement comprising heat treating said hot-rolled band at a temperature between 1450 F. and 1750 F. to place the carbon in solution, drastically quenching from such temperature at a rate at least greater than 75 F./ sec. to a temperature less than 1000 F. to prevent the agglomeration of carbides at the grain boundaries and then holding the hotrolled band within the range of 600 F. to 900 F. for 1 to minutes for sufiicient time to develop lenticular precipitates within the grains prior to cold reducing and annealing said band to develop a grain-oriented structure therein.

13. In the method of producing grain-oriented electrical steel which includes hot-rolling silicon steel containing at least .01 percent carbon and about 2.75 to 3.50 percent silicon to produce a hot-rolled band and thereafter cold reducing and annealing said band to develop a grainoriented structure therein, the improvement comprising heat treating said band at a temperature between 0 F. and 1750 F., drastically quenching from such temperature at a rate in excess of 120 F./sec. to about 800 F. to prevent the agglomeration of carbides at the grain boundaries and then holding the hot-rolled band at about 800 F. for about 10 minutes to develop lenticular precipitates Within the grains prior to cold reducing and annealing said band to develop grain orentation.

14. In the method of producing grain-oriented electrical steel characterized by improved grain orientation and magnetic properties which includes hot-rolling silicon steel consisting of .04 to .065 percent carbon, 15 percent maximum manganese, 2.75 to 3.50 percent silicon with the balance iron and residual amounts of other elements to produce a hot-rolled band having a gauge of .075 to .090 inch, cold reducing the pretreated band to between .020 to .030 inch'gauge, continuously annealing at a temperature between 1600 F. and 1725 F., cold reducing to final gauge, continuously annealing at a temperature between 1400 F. and 1500 F. in an atmosphere containing at least 2 percent water vapor to reduce the carbon content below .003 percent and thereafter box annealing at a temperature above 2000 F. to develop a grain-oriented structure therein having enhanced magnetic properties, the improvement comprising bringing said hot-rolled band to a temperature between 1450 F. and 1750 F. to place the carbon in solution, drastically quenching it from such temperature at a rate of about F./sec. to about 800 F. to maintain the carbon in solution and prevent the agglomeration of carbides at the grain boundaries and holding at about 800 F. for about 10 minutes to develop lenticular precipitates within the grains prior to cold reducing and annealing to develop grain orientation.

15., In the method of producing grain-oriented electrical steel which includes hot-rolling silicon steel containing .04 to .065 percent carbon, .15 percent maximum manganese, 2.75 to 3.50 percent silicon with the balance substantially iron to produce a hot-rolled band having a gauge of. .075 to .090 inch and thereafter cold reducing and annealing said hot-rolled band to develop a grain oriented structure thereimthe improvement comprising finishing said hot rolling at a temperature above 1700 F.

to provide a structure having the carbon in solution, thereafter drastically quenching it at a rate in excess of 120 F. per second to a temperature less than 1000 F. to maintain the carbon in solution and prevent the aglomeration of carbides at the grain boundaries, coiling said band at such temperature and then slowly cooling in coil form to less than 600 F. to develop lenticular precipitates within the grains prior to cold reducing and annealing said band to develop a grain-oriented structure therein.

16. In the method of producing grain-oriented electrical steel characterized by improved grain orientation and magnetic properties which includes producing silicon steel consisting of .04 to .065 percent carbon, .15 percent maxi mum manganese, 2.75 to 3.50 percent silicon with the balance iron and residual amounts of other elements to produce a hot-rolled band having a gauge of .075 to .090 inch, cold reducing the pretreated band to between .020 to .030 inch gauge, continuously annealing at a temperature between 1600 and 1725 F., cold reducing to final gauge, continuously annealing at a temperature between 1400 and 1500 F. in an atmosphere containing at least 2 percent water vapor to reduce the carbon content below .003 percent and thereafter box. annealing at a temperature above 2000 F. to develop a grain-oriented structure therein having enhanced magnetic properties, the improvement comprising finishing hot rolling said band at a temperature above 1700 F. to have the carbon in solution, drastically quenching it at a rate of about 150 F./ sec. to about 800 F. to maintain the carbon in solution and prevent the agglomeration of carbides at the grain boundaries and holding at about 800 F. for about 10 minutes to develop lenticular precipitates Wthin the grains prior to cold reducing and annealing to develop grain orientation.

References Cited in the file of this patent UNITED STATES PATENTS 2,140,374 Yensen et al Dec. 13, 1938 2,307,391 Cole et a1. Jan. 5, 1943 2,765,746 Maxwell Oct. 2, 1956 3,069,299 Fiedler Dec. 18, 1962 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No., 3 151 OO5 September 29 1964 Harry Mi. Alworth et a1 It is hereby certified that. error appears in the above numbered patent req'liring correction and that the said Letters Patent should read as corrected below.

Column 2, line 55 for vary" read very column 8, line 39 for "'orentation" read orientation line 43, for "15 read l5 column 1O line l9 for "'2fl65fl46" read Signed and sealed this 19th day of January 1965,

3T W. SWIDER I V EDWARD J. BRENNER g Officer 1 Commissioner of Patents 

7. A METHOD OF PRODUCING GRAIN-ORIENTED ELECTRICAL STEEL COMPRISING HOT-ROLLING SILICON STEEL CONSISTING OF .04 TO .065 PERCENT CARBON, .15 PERCENT MAXIMUM MANGANESE, 2.75 TO 3.50 PERCENT SILICON WITH THE BALANCE IRON AND RESIDUAL AMOUNTS OF OTHER ELEMENTS TO PRODUCE A HOTROLLED BAND HAVING A GAUGE OF .075 TO.090 INCH, BRINGING SAID BAND TO A TEMPERATURE BETWEEN 1450*F. AND 1750* F. TO PLACE THE CARBON IN SOLUTION, DRASTICALLY QUENCHING FROM SUCH TEMPERATURE AT A RATE OF ABOUT 150*F./SEC. TO ABOUT 800*F. TO MAINTAIN THE CARBON IN SOLUTION AND PREVENT THE AGGLOMERATION OF CARBIDES AT THE GRAIN BOUNDARIES, HOLDING AT ABOUT 800*F. FOR ABOUT 10 MINUTES TO DEVELOP LENTICULAR CARBIDES WITHIN THE GRAINS, COLD REDUCING THE PRETREATED BAND TO BETWEEN .020 TO .030 INCH GAUGE, CONTINUOUSLY ANNEALING AT A TEMPERATURE BETWEEN 1600* F. AND 1725*F., COLD REDUCING TO FINAL GAUGE, CONTINUOUSLY ANNEALING AT A TEMPERATURE BETWEEN 1400*F. AND 1500*F. IN AN ATMOSPHERE CONTAINING AT LEAST 2 PERCENT WATER VAPOR TO REDUCE THE CARBON CONTENT TO LESS THAN .003 PERCENT AND THEREAFTER BOX ANNEALING AT A TEMPERATURE ABOVE 2000*F. TO DEVELOP A GRAIN-ORIENTED STRUCTURE THEREIN HAVING ENHANCED MAGNETIC PROPERTIES. 